Most transformers for battery chargers and laptops adapt to either 240 V. 50Hz or 120V 60Hz. In this case you only need a plug adapter to match the plugs.

You can get International converters to convert from 240 to 120 V. but the cycles remain at 50Hz.
This difference in cycles may cause the motor in your 60 Hz. North American appliance to operate slightly slower when used on 50 Hz. foreign electricity. This cycle difference will also cause analog clocks and timing circuits that use Alternating Current as a timing base to keep incorrect time. Most modern electronic equipment including battery chargers, computers, printers, stereos, tape and CD players, VCR/DVD players, etc. will not be affected by the difference in cycles. Source: TheTimeshareBeat.com/A>